(1) Field of the Invention
The present invention relates to a method for measuring the convergence of a color cathode ray tube (CRT). More particularly, the invention relates to a method for measuring with a high degree of precision the convergence of a color CRT which uses a combination pattern of Red(R), Green(G), and Blue(B) colors on a white pattern when measuring convergence by using a color camera.
(2) Description of the Related Art
In general, in order to display in perfect color the displayed image in the manufacturing process of a color CRT to be used as a display device (e.g., a color TV or a color monitor), three electron beams, i.e., three color (Red, Green, and Blue) electron beams (hereinafter referred to as R.G.B beams) are generated from three electron guns. The beams are ideally concentrated on one pixel point of a CRT screen, each with a different incidence angle. The operation that provides this concentration of the three electron beams is referred to as convergence alignment.
There are two kinds of convergences, a static convergence and a dynamic convergence. The static convergence prevents misconvergence by adjusting the concentration of the R.G.B beams in the vicinity of a center portion of the screen, while dynamic convergence adjusts the concentration of R.G.B beams in the vicinity of a peripheral part of screen.
In a conventional color CRT, a horizontal deviation magnetic field is derived from a deviation yoke mounted between three electron guns, and the screen ideally provides strong pincushion-type magnetic field, while a vertical deviation magnetic field ideally comprises a strong barrel-type magnetic field. Each progression direction of the three(R.G.B) beams is varied by the horizontal and vertical magnetic fields, so that the three(R.G.B) beams are concentrated on a screen.
In order to measure the convergence of color onto the CRT, the prior art provides for scattering of many white patterns with a mixed color selected among Red, Green, and Blue on a color CRT. A color camera picks up the images and divides Red(R), Green(G), and Blue(B) colors from the picked-up image, measures relative distances between Red(R), Green(G), and Blue(B) signals, and calculates convergence.
However, this convergence measuring method using a white pattern cannot reproduce pure Red(R), Green(G), and Blue(B) colors, without any mixed colors, by using the fluorescent material of a standard color CRT. Accordingly, if the color is derived from the image being picked up by a color camera, a mixed color among R.G.B. colors results, as shown in FIG. 1 (i.e., a mixture of Red and Green or a mixture of. Green and Blue). Such a mixed color decreases the precision of convergence measurement.
Accordingly, in order to prevent deterioration in the degree of precision of the signal convergence measurement resulting from the mixed color among R.G.B. colors, the circular R.G.B. patterns shown in FIG. 2 are sequentially displayed in a virtual cross-hatch pattern on the screen of the color CRT, and a camera picks up each of the R.G.B. patterns three times, thereby obtaining a convergence. However, this conventional technique individually picks up each color pattern of R.G.B. patterns, thereby requiring the pick-up operations to be repeated three times. As a result, convergence measuring time is relatively prolonged, and errors due to time differences between image transfers cases occurs because a weight center point is inferred from several different images picked up at different times.
In addition, when displaying a red(R) color pattern, a green(G) color pattern, and a blue(B) color pattern, respectively, it is difficult to accurately position these patterns on a crossing point of a virtual cross-hatch pattern because these patterns have a round shape. As a result, convergence measurement errors occur.
Accordingly, the present invention is directed to an improved method for measuring color signal convergence of color signals of a color CRT. The method is as follows. Two color signals selected from among red(R), green(G), and blue(B) signals are mixed. Two test patterns based on the two color signals on a color CRT screen are generated in sequence. Images of the two test patterns formed on the screen are independently obtained. A signal from each independently obtaining pattern image is converted into image information, and the image information is stored. Finally, a convergence of the image information for each stored test pattern is calculated.
Preferably, the two test patterns are a mixed color pattern of red(R)/blue(B), and a mixed color pattern of green(R)/blue(B). The test pattern contacts a cross point of a cross-hatch pattern, the pattern is positioned to remain unseparated from the cross-hatch pattern, and the pattern is of a triangular shape.